Abstract
Abstract. A case study is presented to test the role several different sources may play in populating the exterior cusp with energetic (E>40 keV) electrons. The properties of the electrons measured in the exterior cusp are compared with the expected signatures of three sources in order to weigh the role each source may contribute in populating this region. The potential sources probed are: (1) solar energetic electrons entering the cusp from the solar wind; (2) an equatorial magnetospheric source with particles drifting to high latitudes on the dayside; and (3) a local source accelerating the electrons in situ. From the observations it is likely that local acceleration is the primary source of the energetic electrons in the exterior cusp during this event.
Highlights
The magnetospheric cusps allow for the most direct entry of shocked solar wind plasma into the magnetosphere (Frank, 1971; Heikkila and Winningham, 1971)
Our results are more consistent with the prediction of Delcourt and Sauvaud (1999) who incorporated an electric field and showed energetic ions that drift to the high latitude dayside are dynamically trapped and will eventually return to the equator
If acceleration in the exterior cusp is efficient enough to be contributing to the energetic particle population along the magnetopause, it could play a role in enhancing the gradient drift entry (GDE) and populating the plasma sheet
Summary
The magnetospheric cusps allow for the most direct entry of shocked solar wind plasma into the magnetosphere (Frank, 1971; Heikkila and Winningham, 1971). The result is a diamagnetic cavity in the exterior cusp In some cases this can bring the magnetic field strength close to 0 nT. Pitch angle distributions of the energetic populations have shown these particles are primarily trapped (Chen et al, 1997; Sheldon et al, 1998), but can show flows traveling along field lines out of the cusp (Whitaker et al, 2006; Walsh et al, 2007). Additional evidence for local acceleration was provided by Chen and Fritz (2001) and Fritz et al (2003) who showed the energetic population was composed of both ionospheric (O+) as well as solar wind (He++, O>+3) ions The presence of both species with similar energies and intensity variability with time indicate a common source.
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